Simian virus 40 (SV40) is capable of producing transformed and tumorigenic cells through the action of the early gene product. Two early gene products have been identified in infected cells, and a third, membrane-associated, antigen is possibly present. The research project involves both the structural analysis of these early proteins to determine their interrelationships and kinetic analyses to determine their time of appearance in infected cells and their intracellular location. Finally, the induction of the host cell by SV40 is being studied to determine what viral functions may be involved in this important cell alteration. The mechanism of host induction is expected to be directly related to the mechanism by which the viral is capable of permanently altering host cells in the process of transformation.